[dmurray]

In trading, it's illegal to do a test trade in production on most regulated exchanges. Making a trade with no intrinsic economic motivation is considered market manipulation and will be punished by the regulator.

It's also illegal not to do such a test trade. Operating a trading system that hasn't been validated under production conditions is reckless behaviour that will be punished by a different arm of the same regulator.

Payments processing seems to be in a similar situation. It's bad practice to test in production, but it's even worse practice not to test in production.